Welding machines are commonly implemented in food can industry for welding can bodies nowadays. In such a welding process, steel sheet is first coated with paint and then carved; the steel sheet then enters a welding machine for welding operation. Once entering the welding machine, carved steel sheet is rolled up to form a cylindrical configuration, and an overlap of 0.3-0.5 mm is formed bet opposing edges of the cylinder body. A welding wheel conductor then welds the overlap along a cope conductor. Paint is finally added to the welded path to complete manufacturing of the steel can. It is thus known that sufficient welding seams for later welding operation must be retained during the coating operation and the welding seams should be kept away from paint contamination, because welding seams being contaminated by paint (either reulted from paint splashes that appear during coating operation or from carving error) will cause notable increment of contact resistance during welding operation and thus cause notable increment of current in the welding machine and anomalous welding teperature. Contaminated seams may also cause jump sparks and poor welding quality, fracture of copper conductor, or break down of welding machine, which all eventually interrupt production line and reduce production capability. Therefore, preventing unqualified steel sheet being contaminated by paint from entering the welding line can help to avoid such damages. An automatic inspecting system is usually provided at entrace of the welding line. Unqualified parts are automatically rejected when the system detects that a welding seam of the steel sheet is contaminated by paint. Such a measure may not only lower defective rate, but also help to prevent from damaging the machine.
Currently, a resistance inspecting device for paint coating continuation on welding seams of steel can sheet is commonly used for inspection purpose. In such a device, a contact inspecting device is provided on the steel sheet carving machine. The inspecting device primarily uses the wheel conductor to measure resistance of welding seams of the steel sheet, where measured resistance values are used as a basis for selecting quaified parts. However, accuracy of such a contact inspecting method is eventually reduced due to contamination of the contact surface after prolong operation.
In view of the above disadvantage of conventional contact resistance inspecting device for paint coating contamination on welding seams of steel can sheet, this invention provides a non-contact continuous photoeletric inspecting device for paint coating contamination on welding seams of steel can sheet. Because the inspecting device of this invention can effectively regulate specifications and quality of incoming material, it greatly enhances competitiveness of metal cans in packaging industry.